1. Field of the Invention
The invention relates to a method and a system which can be used for fitting hearing aids to individuals, for training individuals in hearing with hearing aids and/or for diagnostic hearing tests of individuals wearing hearing aids.
2. Description of Related Art
A hearing aid is a device for compensating a hearing loss of an individual using it. There are various tasks in regard to providing individuals with hearing aids. Two important ones are fitting and hearing training. During a fitting, a hearing aid is adapted to the hearing loss and preferences of the individual. During a hearing training, the individual learns to hear with the hearing aid. Typically, both tasks involve presenting calibrated acoustic stimuli to the individual and obtaining responses in regard to the stimuli to determine hearing performance, needs and preferences.
There are two distinct ways known for presenting stimuli to users of hearing aids: Firstly, stimuli may be presented by room loudspeakers, also referred to as free-field loudspeakers, thereby generating a sound field to which the hearing aid microphones are exposed. Such solutions are disclosed by Bismuth and Revit, as referenced below. Secondly, stimuli may be fed directly into the hearing aid circuit, such that there is no external sound field. Such solutions are commonly referred to as “in-situ” and are disclosed by Lindemann, Chalupper, Hempel and Heller, as referenced below.
French Patent FR 2664494 by Bismuth discloses a method for adjusting an auditory prostheses. Audiovisual scenes are presented to a patient in a soundproof audiometry booth.
U.S. Pat. No. 7,340,062 B2 by Revit et al. discloses assessing real-world performance of hearing aids. Sounds recorded in a real world acoustic environment are presented in a testing environment. A plurality of loudspeakers are located about a listening position or “sweetspot” where the test subject is placed.
U.S. Pat. No. 6,118,877 by Lindemann et al. discloses a hearing aid with in situ testing capability. The hearing aid has a tone generator for providing tones for diagnostic tests. A memory in the hearing aid may store real world sounds to simulate actual usage of the hearing aid. An external test tone generator may be coupled to the hearing aid by a wire.
European Patent Application EP 1 516 584 A1 and corresponding U.S. Patent Application Publication 2005/0059904 A1 by Chalupper et al. disclose a method to be used in the fitting of hearing aids. Chalupper avoids a soundproof booth by monitoring environment sounds and by determining if the noise level at the eardrum is sufficiently low for an in-situ audiometry, i.e., an audiometry in which the hearing aid presents the test tones.
European Patent Application EP 1 912 476 A2 corresponds and corresponding U.S. Patent Application Publication 2008/0124685a1 also by Chalupper disclose a method for training auditory skills, wherein the hearing aid presents sound examples to the user.
German Patent Application DE 10 2009 048 071 A1 by Hempel et al. discloses an improved in-situ fitting. Stimuli are filtered to simulate a predetermined room acoustics which is otherwise missing in in-situ stimuli.
International Patent Application Publication WO 2007/09287 A2 by Heller et al. discloses an in-situ audiometry. Sound samples are fed wirelessly into the hearing aid.
For the sake of completeness, it is mentioned here that feeding signals non-acoustically into hearing aids is not only known from the above in-situ testing, fitting and training methods, but also from real-life applications such as listening to a church service, communicating over a telephone or watching television. The latter is, for example, disclosed in European Patent Application EP 1 571 879 A2 and corresponding U.S. Pat. No. 7,372,970 B2. by Ach-Kowalewski.
An important topic for the present invention is the so called “direct sound”. As used hereinafter, “direct sound” is to be understood as sound which passes directly, i.e., not through the hearing aid microphone, circuit and receiver, from the environment to the eardrum, for example, through a vent of the earpiece of the hearing aid and/or through a leakage path between the earpiece and the skin of the ear canal of the individual wearing the hearing aid. Accordingly, when the hearing aid is in-situ and switched off, there is only the direct sound in front of the eardrum. If it is switched on, there is a mixture of direct sound and receiver sound.
In particular, as used hereinafter, “direct sound” also includes reflected sound, i.e., sound which has be reflected prior to reaching the eardrum.
International Patent Application Publication WO 2007/099116 A2 and corresponding U.S. Pat. No. 8,433,087 B2 by Nordahn disclose a method of compensation for direct sound in hearing aids. A hearing aid gain is adjusted to a value that differs by a predetermined margin from a direct transmission gain calculated for the hearing aid.